1. Field of the Invention
The present invention relates to a developing agent for developing an electrostatic charge image or a magnetic latent image in electrophotography, electrostatic printing, magnetic recording and the like.
2. Description of the Related Art
In the related-art production method of an electrophotographic toner, a kneading pulverization method was the main current. In the case of a toner particle to be produced by the kneading pulverization method, in general, its shape was amorphous, and its surface composition was heterogeneous.
In recent years, with the diffusion of a digital color system aiming at a high image quality, needs for realizing a small particle size have increased. The small-sized toner is able to increase a coverage on a medium such as paper at a low consumption amount of toner and is especially advantageous for colorization of electrophotography. Also, from the viewpoint of enhancing transfer properties and fixability, it has been demanded to precisely control a toner particle regarding the toner shape, particle size distribution and encapsulation and the like. As a production method which meets these demands, the production of a toner by a polymerization method is exemplified.
As the production of a toner by a polymerization method, there are an emulsion polymerization coagulation method, a suspension polymerization method, a solution suspension method and the like. Among these methods, in order to meet the foregoing precise control of a toner particle, an emulsion polymerization coagulation method is advantageous.
In the production method of a toner by employing an emulsion polymerization coagulation method, as a production step of a binder resin, according to the related-art method, a monomer micelle is first produced from an emulsifier, styrene, an acrylic ester, acrylic acid and pure water by using a homogenizer.
Next, pure water and an emulsifier are charged in a polymerizer and sealed with nitrogen. When the internal temperature reaches a prescribed temperature, an aqueous solution of a polymerization initiator is added, and the addition of the previously prepared monomer micelle is rapidly started. After the dropwise addition for a prescribed time, ripening is further performed for a prescribed time.
The residual initiator aqueous solution is added, and ripening is further performed for a prescribed time.
Thereafter, the thus synthesized emulsion is formed into a toner by a method of adding a surfactant in a pigment/wax mixed solution and adding a coagulating agent.
By employing this production method, in the production step of a binder resin, it is possible to reduce the residual monomer which not only imparts a monomer odor and undesirable tackiness to the binder resin but causes filming of the toner, conveyance failure and so on. However, this method took a long ripening time and was poor in efficiency. Also, this method required the new addition of a large amount of the coagulating agent and was large in an environmental load.